Disc drives are used as primary data storage devices in modern computers and computer networks. A typical disc drive includes a head-disc assembly (HDA) housing one or more magnetic discs which are rotated by a spindle motor at a constant high speed and accessed by an array of read/write heads which store data on tracks defined on the disc surfaces. Electronics used to control the operation of the HDA are provided on a printed wiring assembly (also referred to as a "circuit board" or "card") which is mounted to the underside of the HDA to complete the disc drive.
To meet the tremendous technical and logistical challenges of remaining competitive in the present market, disc drive manufacturers have taken steps to design and release new disc drive products as fast and efficiently as possible. Of particular interest is component standardization, which involves the standardization of disc drive designs so that a wide variety of disc drive products from a single product family can be provided with the same or similar hardware components. The performance of each individual drive is then optimized during manufacturing through the selection of parameter values (such as write current, gain, filter characteristics, etc.) which are subsequently loaded and used by the drive during, operation.
As modern disc drives typically employ firmware to provide programming for disc drive controllers (such as microprocessors and digital signal processors), manufacturers further commonly load substantially the same firmware on all of the drives in the same disc drive product family. The firmware relies upon additionally stored information indicative of the particular configuration of the drive (such as the number of discs, the data storage capacity, the type of interface, etc.) to access particular routines suitable for each particular disc drive configuration, and loads the parameters established during manufacturing to optimize the performance of the drive.
A typical disc drive includes one or more non-volatile memory devices (i.e., memory devices that retain their contents when external power is removed from the drive) to which the firmware is written. The parameter values and product information are also written to such devices during the manufacture of the drive. The devices are located on the disc drive printed wiring assembly (PWA) and are accessed during each initialization of the drive.
A problem can thus arise when an originally installed PWA is removed from a disc drive and replaced with a new, replacement PWA. Such replacements commonly occur during manufacturing and field service operations in response to, for example, the detection of a failure condition associated with the originally installed PWA. Unless steps are explicitly taken to ensure that the parameter values and product information associated with the HDA are transferred from the originally installed PWA to the new, replacement PWA, an error condition may result when the disc drive is reinitialized using the new PWA. Particularly, the firmware stored on the new PWA may expect to see a different hardware configuration than that which the HDA actually possesses, or the parameter values stored on the new PWA may be inappropriate for reliable operation of the drive. Moreover, during manufacturing, a disc drive can often spin up with a default code before the new or unique code may be downloaded.
Such mismatches in parameters and product information can result in unacceptable delays as a disc drive with a newly installed replacement PWA attempts to reinitialize. Moreover, when such mismatches in parameters and product information are sufficiently pronounced, the disc drive can be physically damaged when the drive attempts to spin-up and load the heads (i.e. operationally move the heads out over the disc surfaces). Although the optimal parameter values for an HDA are also typically stored on designated tracks of the HDA, such tracks cannot be accessed until after the disc drive has already successfully spun-up and loaded the heads.
Even when no replacement of the PWA occurs, problems can still arise when new, updated firmware is downloaded to the PWA, if the new firmware is incorrectly suited to the configuration of the HDA. Such firmware updates are often performed during field service operations, and although precautions are taken to ensure the correct firmware is downloaded, errors still occasionally occur. As will be recognized, a firmware-hardware mismatch can also result in the same types of problems that occur when an incorrectly configured PWA is installed.
For example, during spin-up, the firmware may not be capable of determining the configuration of a particular HDA if the number of heads and discs in a disc drive differ depending upon the drive. In an effort to reduce costs, many manufacturers may create disc drives utilizing a reduced number of heads and discs. For example, disc drives may comprise five heads for three discs (commonly referred to as a depopulated configuration) as opposed to ten heads for five discs (commonly referred to as a fully populated configuration). In both configurations, the same hardware including an actuator with six arms extending therefrom may be used such that no additional costs are accrued during manufacturing a depopulated configuration of a disc drive. The balance and inertial characteristics of a depopulated actuator can be maintained by the use of dummy heads suspended from the actuator, through the use of swage plates with extra mass to compensate for the missing flexures and heads, and other suitable approaches.
Although cost is significantly reduced, a problem arises when firmware is not capable of adapting to the depopulated configuration of the disc drive during initialization of the drive. Therefore, when the firmware of the PWA sends incorrect initialization information, disc drive fault or even damage to the HDA may result.
Accordingly, there is a need for a way to readily indicate the configuration of the HDA of a disc drive to eliminate problems when a new, replacement PWA is installed in the drive, or when new firmware is downloaded to the PWA.